The subject matter disclosed herein relates to over-current protection for power circuits. More specifically, the subject matter disclosed herein relates to a simple and efficient over-current protection assembly that enables the use of multiple contacts in parallel & series to disconnect high voltages and/or currents resulting in improved breaking performance.
Over-current protection devices provide electrical protection and/or isolation to electrical systems. Examples of over-current protection/isolation devices include but are not limited to circuit breakers, interrupters, switches, contactors and the like. Although there are slight differences in the operation and/or application of these devices, they perform substantially the same basic function of protecting and/or isolating an electrical system whenever an electrical abnormality or normal load switching occurs in any part of the system. The above-described terms are used interchangeably in the present disclosure to refer broadly to over-current protection devices and/or assemblies. Accordingly, it is intended that any part of this disclosure that makes specific reference to one type of over-current protection device and/or assembly applies equally to other types.
Circuit breakers are a well-known over-current protection device. Circuit breakers come in a wide variety of sizes and configurations, based primarily on the characteristics and needs of the electrical system that the circuit breaker is designed to protect. One example of a known circuit breaker configuration is a rotary contact circuit breaker. In a rotary contact circuit breaker, current enters the electrical system from a power line. The current passes through a load strap to a stationary main contact fixed on the strap, and then to a moveable main contact. The moveable main contact is fixedly attached to an arm, and the arm is mounted to a rotor that is rotatably mounted in a cassette.
As long as current passing through the load strap is below a predetermined level, the fixed contact remains in physical contact with the moveable main contact, and the current passes from the fixed main contact to the moveable main contact and out of the circuit breaker to down line components of the electrical system. However, if an extremely high over-current condition occurs (e.g., a short circuit), electromagnetic forces are generated between the fixed and moveable main contact pair. These electromagnetic forces repel the movable main contact away from the fixed main contact. Because the moveable main contact is fixedly attached to a rotating arm, the arm pivots and physically separates the fixed main contact from the moveable main contact, thus tripping the unit, breaking the flow of current and isolating down line components.
An arc is generated when contacts separate and the current path is interrupted. Different circuit breakers use vacuum, air, insulating gas or oil inside the circuit breaker chamber to contain, cool and extinguish arcs in a controlled way. This allows the gap between contact pairs to again withstand the voltage in the circuit. In addition to the above-described main contact pairs, known circuit breaker configurations also provide arc contact pairs that assist in controlling arcs by providing a path for arc currents to be absorbed when the main contact pair is opened. In some circuit breaker configurations, the main contact pair handles both main and arc currents.
It has been proposed to provide over-current protection devices having multiple main and/or arcing contacts. In such devices, each fixed/movable contact pair requires its own separate and relatively complex mechanism for opening and closing the contacts. The need for a separate opening/closing mechanism for each contact pair generally increases the cost, device footprint and operational inefficiency of known multi-contact over-current protection devices. In some cases, the variance in opening times and geometry of the extra linkages requires additional electrical parts to equalize arc voltages across the contacts that are arranged in series.